The present invention relates generally to printed circuits, and more specifically, to components employed in the manufacturing of printed circuit boards.
In recent years, printed circuit components have become widely used in a variety of electronic devices. Of particular interest are multi-layer, printed circuit board components that have been developed to meet the demand for miniaturization of electronic components and the need for printed circuit boards having a high density of electrical interconnections and circuitry. In the manufacture of printed circuit boards, conductive foils (which are usually copper foils) are secured to a core that is conventionally a reinforced or non-reinforced dielectric. (Throughout this specification, the use of the term xe2x80x9ccorexe2x80x9d is meant to include any one of a variety of core materials, all of which may be reinforced or non-reinforced and may include an epoxy, polyester, polyimide, a polytetrafloroethylene, and in some applications, a core material which includes previously formed printed circuits). The process of forming the printed circuits includes one or more etching steps in which the undesired or unwanted copper is removed by etching away portions of the conductive foil from the component surface to leave a distinct pattern of conductive lines and elements on the surface of the etched component. The etched component and other component materials may then be packaged together to form a multi-layer circuit board package. Additional processing, such as hole drilling and component attaching, will eventually complete the printed circuit board product.
The trend in recent years has been to reduce the size of electronic components and provide printed circuit boards having, as one example, multi-chip modules. This results in a need to increase the density of components, such as surface-mount components, provided on the printed circuit board. This in turn results in a so-called xe2x80x9cdensely populatedxe2x80x9d or simply xe2x80x9cdensexe2x80x9d printed circuit board.
A key to providing a densely populated printed circuit board is to produce close and fine circuit patterns on the outer surfaces (i.e., the exposed surfaces) of the resulting multi-layer printed circuit board. The width and spacing of conductive paths on a printed circuit board are generally dictated by the thickness of the copper layer used thereon. For example, if the copper layer has a thickness of 35 xcexcm (which is a conventional 1-ounce foil used in the manufacture of many printed circuits), exposing the printed circuit board to an etching process for a period of time to remove such a foil thickness will also reduce the width of the side areas of the printed circuit path by approximately one-half to one-third. In other words, a printed circuit board must be designed to take into account the original thickness of the copper and that an etching process will also eat away the sides of a circuit path (i.e., undercut a masking material). Thus, the thickness of the circuit lines, and the spacing therebetween, is basically limited by the thickness of the copper used on the outer surface of the multi-layer printed circuit board. To produce xe2x80x9cdensely populatedxe2x80x9d printed circuit boards, it is therefore necessary to reduce the thickness of the copper, at least on the outermost surface of a multi-layer printed circuit package. The thickness of the copper foil sheet is generally limited by the ability of a foil manufacturer to handle and transport such sheets. In this respect, as the thickness of the foil decreases below 35 xcexcm, the ability to physically handle such foil becomes more difficult.
The present invention overcomes this and other problems and provides a use in components for forming printed circuit boards, wherein the component has an extremely thin copper layer on a support layer, wherein both layers are usable in forming printed circuits.
In accordance with the present invention, there is provided a component for use in forming a printed circuit board. The component is comprised of a copper foil having a layer of a chromium-containing material deposited thereon. The layer of chromium-containing material has a thickness of up to about 0.10 xcexcm. A layer of electrodeposited copper is provided on the layer of chromium. The layer of electrodeposited copper has a thickness of less than 35 xcexcm. A nodular treatment is applied to the copper foil and to the electrodeposited copper.
In accordance with another aspect of the present invention, there is provided a component for use in forming a printed circuit board, comprised of a copper foil and a metal-containing release layer on one surface of the copper foil. The metal-containing release layer has a thickness of up to about 0.10 xcexcm. A layer of copper is electrodeposited on the metal-containing release layer, the layer of electrodeposited copper having a thickness of less than about 35 xcexcm. A nodular treatment is applied to the copper foil and to the electrodeposited copper.
In accordance with another aspect of the present invention, there is provided a method of forming a component for use in manufacturing printed circuits comprising the steps of:
cleaning one surface of a copper foil by exposing a surface of a copper foil to an acid solution to remove oxide film from the surface;
rinsing the surface of the copper foil to remove residual acid solution;
electrolytically depositing a layer of chromium on the surface of the copper foil, the layer of chromium being less than about 0.10 xcexcm;
cleaning the layer of chromium;
electrodepositing a layer of copper on the chromium layer, the layer of copper having a thickness less than about 35 xcexcm; and
applying a nodular treatment layer to the copper foil and to the layer of copper.
In accordance with another aspect of the present invention, there is provided a method of forming printed circuits, comprising the steps of:
(a) applying a metal-containing release layer that is less than about 0.10 xcexcm onto a clean surface of a copper foil;
(b) electrodepositing a layer of copper that is less than about 35 xcexcm onto the metal-containing release layer;
(c) applying a nodular treatment layer to the copper foil and to the layer of copper.
(d) bonding the copper foil to a first prepreg layer and the layer of copper to a second prepreg layer; and
(e) separating the prepreg layers such that the copper foil separates from the layer of copper along the metal-containing release layer.
It is an object of the present invention to provide a flexible component for use in forming printed circuits.
Another object of the present invention is to provide a component for use in forming a printed circuit, wherein the component has an exceptionally thin layer of copper mounted onto a support layer of copper.
Another object of the present invention is to provide a component as described above wherein both layers of copper are usable in forming a printed circuit.
A still further object of the present invention is to provide a component as described above wherein both layers of copper have a nodular treatment on the surface thereof for better adhesion.
Another object of the present invention is to provide a method of forming a printed circuit board using a component as described above.
These and other objects and advantages will become apparent from the following description of preferred embodiments of the invention, taken together with the accompanying drawings.